CONSOLIDATED STATEMENTS OF COMPREHENSIVE INCOME - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Net income (loss)	$ 737.3	$ (173.7)	$ 433.6
Pension Plan and Restoration of Retirement Income Plan:
Amortization of prior service cost, net of tax of $0.0, $0.0 and $0.0, respectively	0.1	0.0	0.0
Amortization of deferred net loss, net of tax of $0.9, $1.2 and $1.1, respectively	1.6	3.9	3.4
Net gain (loss) arising during the period, net of tax of $0.0, ($1.7) and ($2.5), respectively	1.4	(5.1)	(8.1)
Prior service cost arising during the period, net of tax of ($0.3), $0.0 and ($0.1), respectively	(1.1)	0.0	(0.2)
Settlement cost, net of tax of $2.7, $0.7 and $2.7, respectively	6.0	2.2	8.6
Postretirement benefit plans:
Amortization of prior service credit, net of tax of ($0.4), ($0.6) and ($0.6), respectively	(1.4)	(1.7)	(1.7)
Amortization of deferred net gain, net of tax of $0.0, $0.0 and $0.0, respectively	0.1	(0.1)	(0.2)
Net loss arising during the period, net of tax of ($0.2), ($0.8) and $(0.1), respectively	(0.7)	(2.4)	(0.2)
Curtailment cost, net of tax of $0.0, $(0.1) and $0.0, respectively	0.0	(0.3)	0.0
Other Comprehensive (Income) Loss, Defined Benefit Plan, Prior Service Cost (Credit), after Tax	(1.1)	0.0	(0.2)
Other comprehensive income (loss), net of tax	7.3	(4.2)	1.0
Other comprehensive gain (loss) from unconsolidated affiliates, net of tax $0.3, ($0.2) and ($0.2), respectively	1.3	(0.7)	(0.6)
Comprehensive income (loss)	$ 744.6	$ (177.9)	$ 434.6